Summary of Work: Neutrophils in whole blood, buffy coats, and those isolated by PercollR gradients have been characterized with respect to Complement receptor type 3 (CR-3) expression. Basal as well as upregulated levels of CR-3 expression have been studied using a mouse monoclonal antibody to CR-3 and goat anti- mouse F(ab')2 fragments using an Ortho 50-H Flow Cytometer to selectively analyze the neutrophil population fluorescence histograms have been generated to discern levels of receptor expression. Preliminary studies have characterized maximal receptor expression. Upregulation due to incubation and isolation procedures have also been monitored. To date no significant difference has been detected in the ability of neutrophils from chemotactically depressed and non-depressed localized juvenile periodontitis patients to upregulate CR-3 compared to the normal population.